This invention relates generally to a process and apparatus for the fabrication of semiconductor devices, and more particularly to processing apparatus utilizing solid reactant sources and to a process for using such apparatus in the fabrication of semiconductor devices.
Chemical vapor deposition (CVD), and especially low pressure chemical vapor deposition (LPCVD) has become an essential process in the fabrication of semiconductor devices. Chemical vapor deposition provides a method for depositing thin conformal films of controlled thickness and composition. CVD has long been used, for example, for the deposition of polycrystalline silicon, silicon dioxide, silicon nitride, doped glasses, tungsten, titanium nitride, and the like. For each of these materials there is a readily available and easily usable reactant source in either gas or liquid form. For example, polycrystalline silicon is chemical vapor deposited by the dissociation of silane, and silicon nitride is chemical vapor deposited by the reaction of dichlorosilane and ammonia. Both silane and dichlorosilane are gases. Tungsten is deposited by the hydrogen reduction of tungsten hexafluoride, a liquid source.
The trend in the semiconductor industry is to fabricate devices with smaller and smaller physical size. As the size of the minimum device feature decreases to less than one micrometer and especially as it decreases to less than 0.5 micrometers, the need arises for the chemical vapor deposition of other materials beyond those commonly used materials enumerated above. For example, as the semiconductor technology advances, there is a need for the chemical vapor deposition of metals such as copper, gold, and other materials such as ferroelectric and superconducting materials. There are no readily available gaseous or liquid reactant sources for the chemical vapor deposition of these materials. Accordingly, because of the need to deposit such materials, solid reactant sources are being investigated. The solid sources which are available for the chemical vapor deposition of materials such as copper and gold, however, have very low vapor pressures. A low vapor pressure reactant source leads to problems of nonuniformity of the deposited film, both across a single substrate and from substrate to substrate within a commonly processed multiwafer lot, because of the limited amount of source vapor that can be supplied to the reaction. The nonuniformity results from source depletion in the reaction zone. Additionally, a low vapor pressure CVD reactant source leads to low reproducibility because of poor control of the reactant materials. In the past, when solid reactant sources have been used, the vapor has been pulled directly from the heated source or has been carried from the reactant source to the deposition reactor by passing a carrier gas over the surface of the source. In either case, the available source vapor is quickly depleted and a limited amount of source is carried to the deposition reactor.
In view of the growing need for solid reactant sources for the chemical vapor deposition of metals, metal oxides, and other materials for which a convenient gaseous or liquid source is not available, a need existed for a source apparatus and for a process for chemical vapor deposition which would utilize a solid reactant source and which would introduce enough reactant vapor into a deposition reactor to achieve acceptable film uniformity and reactor throughput, especially for the fabrication of semiconductor devices.
It is therefore an object of this invention to provide an improved process for chemical vapor deposition from a solid reactant source material in a controlled and consistent manner.
It is a further object of this invention to provide an improved method for fabricating a semiconductor device including chemical vapor deposition from a solid reactant source.
It is yet another object of this invention to provide an improved solid reactant source for a chemical vapor deposition reaction.